1. Field of the Invention
The present invention pertains to apparatus and methods for forming a fluid tight plug in fluid conduits such as fluid transmission pipelines wherein a relatively small diameter hole is formed in the line and a flexible bag inserted into the line through the hole. The flexible bag is filled with a liquid which is frozen by circulating a cryogenic cooling fluid around the exterior of the line in the vicinity of the bag and/or circulating the cooling fluid through a conduit disposed within the bag.
2. Background Art
The present invention pertains to an improved method and apparatus for providing plugs in conduits such as fluid transmission lines for purposes of installation, repair, modification and hydrostatic testing of the lines. The formation of a temporary substantially fluid tight seal or plug in a fluid transmission line and the like by freezing a slug of liquid within the line is a viable process and one successful method is disclosed in U.S. Pat. No. 3,827,282 issued Aug. 6, 1974 to B. D. Brister. Improved apparatus for carrying out various processes in forming a plug of frozen liquid in a section of a pipeline or the like are disclosed in U.S. Pat. Nos. 4,112,706 and 4,220,012 to Brister.
The aforementioned patents contemplate the formation of a frozen slug of liquid which may be formed using the liquid in the pipeline itself or by injecting a quantity of water into the line and freezing the water slug. However, there are certain instances wherein water cannot be injected into the line because of the possibility of contaminating the pipe and the product carried thereby. Moreover, the condition or particular construction of the line may not permit the injection and transmission of the water slug to the site where the plug is to be formed. There are also, of couse, instances wherein pipelines need the provision of a substantially fluid tight seal to be formed, which pipelines contain a product which cannot be suitably frozen to form a reliable plug in the line.
It is known in the art of providing plugs for pipelines and the like to tap a hole in the side of the line for the insertion of a flexible bag which is filled with a gas such as air to expand the bag into sealing engagement with the inner wall of the pipe to form a seal. However, known techniques for forming pipeline seals with the installation of flexible bags require also that a mechanical stop or abutment be provided since the engagement force between the bag and the pipe wall is not sufficient to hold against high fluid pressures in the line. Moreover, disadvantages of known flexible bag plugging techniques include the requirement of relatively expensive equipment, particularly the need for the mechanical backstop or abutment, as well as the provision of fairly closely spaced multiple holes in the pipeline which tend to weaken the pipe structure and require that additional repair fittings be used. The abovementioned type of pipeline plugging method is not only expensive, as previously mentioned, but it is limited to relatively low pressure applications.
The present invention largely overcomes the problems of providing suitable pipeline plugging means in lines which cannot be filled with water and frozen, or do not contain a fluid which may be suitably frozen to form a plug. The present invention also provides improvements in apparatus and techniques wherein a hole is formed in the pipeline and wherein means are inserted from the exterior of the pipe to form a plug which may then be removed upon completion of the operation for which the plugging was required.